The present invention relates to a catalyst based on Vanadium, its preparation and its use in the (co)polymerization of xcex1-olefins.
More specifically, the present invention relates to a catalyst consisting of a Vanadium complex, a co-catalyst based on Al alkyl and, optionally, a reactivator. In addition, the present invention relates to a process for the (co)polymerization of xcex1-olefins in the presence of said catalyst.
At present catalysts based on Vanadium consist of a Vanadium complex, an Al alkyl and a chlorinated reactivator. The Vanadium complex is the precursor of the active species which is formed by interaction with the Al alkyl. This species initiates the polymerization but is also easily deactivated by the same Al alkyl, producing a reduction in activity. The reactivator has the function of re-establishing the active species guaranteeing a longer life-time of the catalyst and consequently a greater catalytic activity (see G. Natta et al., Makromol. Chem., 81, 161-172 (1965; E. Adisson, J. Pol. Sc., art A: Polymer Chemistry, Vol. 31, pages 831-839, 1993). In order to have catalytic activity, however, at least one of the reagents must be chlorinated (see G. Natta et al., J. Polym. Sc., Vol. 51, 411-427, 1961). In fact systems such as V(acac)3/AlEt2Cl or VC14/Al(C6H13)3 are active in the copolymerization of ethylene with propylene, whereas other systems without chlorine such as V(acac)3/Al (i-Bu)3 and V(acac)3/AlMe3 do not give a polymer, but become active when a chlorinated reactivator such as Cl3CCOOR, CCl4 is added to the system (see E. Adisson et al. J. Pol. Sc., Part A, Polymer Chemistry, Vol. 32, pages 1033-1041, 1994).
The presence of chlorine in the catalytic system is particularly harmful in the case of the production of ethylene-propylene elastomeric copolymers (EPR and EP(D)M) with a process in suspension which does not comprise a purification phase from the catalytic residues and in particular chlorine. This inevitably causes a lower purity of the products and consequently excludes use in particular applicative fields (for example cables). In addition, the presence of inorganic chlorine in the polymer may develop hydrochloric acid during the processing of the polymer making it necessary to use anti-acid additives, with a consequent increase in the running costs.
The request for catalytically active Vanadium catalysts in the presence of the smallest possible quantity of chlorine, with activities comparable to or higher than those of the known art, therefore remains unsatisfied.
A new group of catalysts capable of giving copolymers containing a small quantity of residual chlorine, has now been found. These catalysts are based on Vanadium complexes having halogenated carboxyl groups as ligands.
A first object of the present invention therefore relates to a Vanadium complex having general formula (I)
(RCOO)nVXpLmxe2x80x83xe2x80x83(I)
wherein R is a monofunctional hydrocarbon radical having from 1 to 20 carbon atoms and from 1 to 6 halogen atoms, selected from chlorine and bromine, preferably chlorine; X is chlorine or bromine, preferably chlorine; L is an electron donor; p+n=3, 4 or 5, preferably=3; n is greater than or equal to 1; m is between 0 and 3.
Examples of Rxe2x80x94COO carboxyl groups in formula (I) are selected from:
1) Rxe2x80x94COO=
xe2x80x83wherein R1, R2, R3, R4 and R5 the same or different, are selected from H, Cl or Br, alkyls, cycloalkyls, aryls, arylalkyls, alkylaryls or alkyls, cycloalkyls, aryls, arylalkyls, alkylaryls containing chlorine or bromine, with the proviso that at least one of the R1-R5 residues is selected from chlorine or bromine, or an alkyl, cycloalkyl aryl, arylalkyl, alkylaryl group containing chlorine or bromine; q varies from 0 to 10.
Non-limiting examples of these derivatives are represented by:
Cl3COO, CCl3CH2COO, CCl3(CH2)2COO, CHCl2COO, CH3CCl2COO, C6H5CCl2CH2COO, (C6H5)2CClCOO, CH3CH2CCl2COO, C6H5CH2CH2CH2Cxe2x80x94HClCOO, ClC6H4CHClCOO, ClC6H4CH2COO, 2-cyclopropyl-2,2-dichloro-acetic acid.
2) Rxe2x80x94COO=
xe2x80x83wherein:
R1, R2, R3 and R4, the same or different, are selected from H, Cl or Br, alkyls, cycloalkyls, aryls, arylalkyls, alkylaryls, or alkyls, cycloalkyls, aryls, arylalkyls, alkylaryls containing chlorine or bromine, with the proviso that at least one of the R1-R4 residues is chlorine or bromine or an alkyl, cycloalkyl aryl, arylalkyl, alkylaryl group containing chlorine or bromine;
r and s vary independently from 0 to 5, with the restriction that r+s is from 1 to 5.
Non-limiting examples of these derivatives are represented by:
Cl3CC6H4COO, ClCH2C6H4COO, ClCH2C6H2Cl2COO, C6Cl5COO
3) Rxe2x80x94COO=
xe2x80x83wherein:
Z, R1, R2, R3, R4, R5, R6, the same or different, are selected from H, Cl, Br, alkyl, cycloalkyl, aryl, arylalkyl, alkylaryl, alkyls, cycloalkyls, aryls, arylalkyls, alkylaryls containing chlorine or bromine, with the proviso that at least one of the Z and R1-R6 residues is chlorine or bromine or an alkyl, cycloalkyl aryl, arylalkyl, alkylaryl group containing chlorine or bromine;
t and u independently vary from 0 to 10, preferably from 0 to 2.
Non-limiting examples of these derivatives are represented by:
CCl3CHxe2x95x90CHCOO, CCl3CClxe2x95x90CClCOO, CCl2xe2x95x90CClCCl2COO.
4) Rxe2x80x94COO wherein R is selected from cycloalkyl, polycycloalkyl, cycloalkenyl, polycycloalkenyl having from 3 to 20 C atoms, substituted with at least one chlorine or bromine or with hydrocarbyl groups containing at least one chlorine or bromine.
Non-limiting examples of these derivatives are represented by:
2-chloro-cyclohexane carboxylic acid, 2,2-dichlorocyclopropane-carboxylic acid, 2,2-3,3-tetrachlorocyclopropane-carboxylic acid, perchlorocyclohexane carboxylic acid, cyclo hex-2-ene-2-trichloromethyl-carboxylic acid.
As far as L is concerned, i.e. the electron donor, typical examples are alkyl and cycloalkyl ethers, alkyl esters of aromatic and aliphatic carboxylic acids, aliphatic ketones, aliphatic amines, aliphatic alcohols. L is preferably selected from tetrahydrofuran (THF), dimethoxymethane, diethoxyethane.
A second object of the present invention relates to the process for the preparation of the complexes having general formula (I) which comprises:
a) treatment of a Tallium (Tl) salt having the general formula RCOOTl, wherein R has the meaning defined above, with a Vanadium halide, preferably VCl3, in an aliphatic or aromatic, ether or chlorinated, hydrocarbon solvent, alone or in a mixture, preferably THF and dimethoxyethane, at temperatures ranging from 0 to 50xc2x0 C., preferably from 15 to 30xc2x0 C., for a time ranging from 30 minutes to 6 hours, preferably from 1 to 4 hours;
b) separation, preferably filtration, of the Tl halide formed by the reaction;
c) isolation of the Vanadium complex.
In the preferred embodiment, step (c) is carried out by evaporation of the solvent or precipitation of the complex by the addition of a suitable precipitating agent, usually a hydrocarbon solvent, preferably pentane.
Typical but non-limiting examples of these syntheses are provided in the experimental section, which describes, among others, the preparation of V(CCl3COO)3 by reaction between VCl3 and Tl(CCl3COO) in a molar ratio 1/3, V(CH2Clxe2x80x94C6H4xe2x80x94COO)3 by reaction between VCl3 an CH2Clxe2x80x94C6H4xe2x80x94COOTl in a molar ratio 1/3, V(CCl3COO)2Cl by reaction between VCl3 and Tl(CCl3COO) in a molar ratio 1/2, V(CCl3CH2CH2COO)3 by reaction between VCl3 and CCl3CH2CH2COOTl in a ratio 1/3.
A third object of the present invention relates to a catalytic system for the (co)polymerization of xcex1-olefins consisting of:
(a) Vanadium complex having general formula (I),
(b) organo Aluminum derivative having general formula (II) AlRnXm, wherein R is a C1-C20 alkyl group, X is chlorine or bromine, preferably chlorine, and n+m=3, with the exclusion of the compound having n=0,
(c) optionally a reactivator, preferably chlorinated. Among the Vanadium compounds having general formula (I), those wherein RCOO has general formula (Ia)
CCl3xe2x80x94(xe2x80x94CH2xe2x80x94)nxe2x80x94COOxe2x80x83xe2x80x83(Ia)
xe2x80x83wherein n is an integer between 0 and 2, i.e. trichloroacetate (n=0), trichloropropionate (n=1), trichlorobutyrrate (n=2), have proved to be particularly effective.
Typical examples of compounds having general formula (II) are AlEt2Cl (diethylchloroaluminum), AlMe3 (trimethylaluminum), AlEt3 (triethylaluminum), Al (i-Bu)3 (triisobutylaluminum).
In the preferred embodiment the cocatalyst having general formula (II) has a C1-C20 alkyl group as R, n=3 and m=0. Even more preferably R is an isobutyl group.
The molar ratio between said cocatalyst having general formula (II) and the catalyst having general formula (I) is between 1 and 500, preferably between 3 and 100, more preferably between 20 and 50.
When, in the cocatalyst having general formula (II), m is different from 0, the preferred cocatalyst is diethylchloroaluminum. When, in the cocatalyst having general formula (II), m=0, the preferred cocatalyst is triisobutylaluminum. In the preferred embodiment the molar ratio cocatalyst and catalyst is between 5 and 10.
As far as the reactivator is concerned, this is usually selected from chlorinated organic compounds, for example ethyl trichloroacetate, n-butyl perchlorocrotonate, diethyl dichloromalonate, carbon tetrachloride, chloroform.
The molar ratio between the possible reactivator and vanadium can vary from 0:1 to 100:1, preferably from 1:1 to 40:1, even more preferably between 1:1 and 10:1.
When, in the cocatalyst having general formula (II), m is different from 0, the preferred reactivator is ethyl trichloroacetate and the preferred molar ratio between reactivator and vanadium is between 4:1 and 10:1.
When, in the cocatalyst having general formula (II), m is equal to 0, the preferred reactivator is carbon tetrachloride and the preferred molar ratio between reactivator and vanadium is between 10:1 and 50:1.
In the preferred embodiment the reactivator is not used.
The catalysts of the present invention can be used in (co)polymerization processes of xcex1-olefins in liquid phase (solution or suspension) at low or medium pressure (15-50 ate) and at temperatures ranging from xe2x88x925 to 75xc2x0 C.
In the preferred embodiment the temperature is between 25 and 60xc2x0 C. and the pressure between 6 and 35 ate.
The polymers and copolymers thus obtained have very high average molecular weights. If the molecular weight is to be regulated to a lower value, hydrogen can be used as molecular weight regulator.
The catalyst for the (co)polymerization of xcex1-olefins and terpolymerization with dienes is prepared by contact of the Al alkyl with the V complex dissolved in an aliphatic or aromatic hydrocarbon solvent and, optionally, with the reactivator. The contact can take place separately without the mixture of olefins to be polymerized for a time ranging from 1 minute to 30 minutes, preferably from 5 to 20 minutes, at a temperature ranging from 0xc2x0 C. to 50xc2x0 C., preferably from 15xc2x0 C. to 40xc2x0 C., or it can take place in the polymerization reactor in the presence of the mixture of monomers. In this case the three reagents can be added separately or as a mixture of two of these. The catalyst is preferably formed xe2x80x9cin situxe2x80x9d by introducing the Al alkyl into the autoclave already containing the solvent (heptane or liquid propylene), the reagent mixture and, optionally, the termonomer and adding the solution of V complex with the possible reactivator in toluene.
The catalysts of the present invention can be used in the polymerization of xcex1-olefins, preferably in the polymerization of ethylene, in the copolymerization of ethylene with propylene and higher xcex1-olefins and in the terpolymerization of ethylene with propylene and dienes to give polymers with a density ranging from 0.96 g/cm3 and 0.86 g/cm3.
The copolymerization of ethylene-propylene to give EPR elastomeric copolymers and the terpolymerization of ethylene-propylene-non-conjugated diene to give EP(D)M rubbers, are particularly preferred.
The diene can be selected from:
alicyclic dienes with a linear chain such as 1,4-hexadiene and 1,6-octadiene;
acyclic dienes with a branched chain such as 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, 3,7-dimethyl-1,7-octadiene;
alicyclic dienes with a single ring such as 1,4-cyclohexadiene, 1,5-cyclo-octadiene;
dienes having condensed and bridged alicyclic rings such as methyltetrahydroindene, 5-ethylidene-2-norbornene (ENB), 5-propenyl-2-norbornene.
In the preferred embodiment the diene is ENB or 1-methylene-2-vinyl-cyclopentane.
The EPR and EP(D)M elastomeric copolymers which can be obtained with the catalysts of the present invention contain from 20 to 65% in moles of propylene and quantities not exceeding 15% of ENB. The weight average molecular weight of the polymer obtained in the presence of hydrogen varies from 50,000 to 500,000.